Hybrid ring network



NOV. 21, 1961 H. T. BUDENBOM 3,010,082

HYBRID RING NETWORK Filed July 25. 1952 m." w n-4.21 a

/N l/E N 7 0/? H 7'. BUDENBOM A 770/? NE V United States Patent3,010,082 HYBRID RING NETWORK Horace T. Budenbom, Short Hills, N.J.,assignor to Bell Telephone Laboratories, Incorporated, New York, N.Y., acorporation of New York Filed July 25, 1952, Ser. No. 300,909 13 Claims.(Cl. 333-9) This invention relates to wave transmission networks andmore particularly to hybrid ring networks.

The object of the invention is to improve the impedance match at certainarms of a five-arm hybrid ring.

A more specific object is to make the input impedances equal at all armsof a five-arm hybrid ring without incurring an appreciable loss ofpower.

A five-arm hybrid ring may be designed to have certain desirableconjugate relationships which may be utilized, for example, in branchingarrangements or in networks for obtaining the complex sum of anddifference between two coherent input voltages or powers. Rings of thistype are disclosed, for example, in the paper by W. A. Tyrrell entitledHybrid Circuits for Microwaves, published in the Proceedings of theI.R.E. for November 1947, and in my copending United States patentapplication Serial No. 52,856, filed October 5, 1942, now Patent No. 2,784,381 issued March 5, 1957. In one embodiment, such a ring comprises aclosed transmission loop having an effective length of wavelengths A ata selected design frequency f and five transmission branches or armsconnected in series with the loop at successive points thereon spacedapart by M4 at the frequency For reference, these arms may be designatedone to five, with a spacing of M2 between the first and the fifth. Theloop and the arms may be constituted by a wave guide, a coaxial cable,or some other suitable type of transmission line. If all of the armshave the same characteristic impedance Z each is terminated in animpedance Z and the loop has a characteristic impedance equal to Z /VZthere will be a good impedance match with the loop for the third arm,but a considerable mismatch for the other arms. In practice, thismismatch has been found to be of the order of three decibels, which isundesirably large for some applications, especially if high powertransmission is involved.

In accordance with the present invention, this mismatch is greatlyreduced, without substantial power loss, by adding a sixth series arm ofcharacteristic impedance Z connected to the loop at a point midwaybetween the first and the filfth arms, iteratively terminating the addedarm, and providing an auxiliary transmission path between the third armand the sixth arm. The addition of this sixth terminated arm only,without the auxiliary path, will provide an impedance match at thefirst, second, fourth, and fifth arms, but a considerable fraction ofthe input power will be lost by dissipation in its termination. Thefunction of the auxiliary path is to prevent this loss of power. In oneembodiment, the third and the sixth arms are connected by an auxiliarypath extending across the loop and having an electrical length equal to)\/4. If a wave guide of the hollow-pipe type is used, it may benecessary to include dielectric material within the guide to provide therequired electrical length. In a second embodiment, the auxiliary pathincludes a directional coupler connecting the third and the sixth arms.

The nature of the invention and its various objects, features, andadvantages will appear more fully in the following detailed descriptionof typical embodiments illustrated in the accompanying drawing, of whichFIG. 1 is a perspective View, partly cut away, of one embodiment of ahybrid ring network in accordance with the invention; and

FIG. 2 is a similar view the invention.

The hybrid ring network shown in FIG. 1 comprises a section oftransmission line 10 formed into a loop or ring and provided with sixequally spaced transmission branches or arms, numbered consecutively 1to 6, and an auxiliary transmission path 7. As shown, the ring and thebranches are made of hollow-pipe wave guide of oblong cross section,adapted to transmit electromagnetic waves having an smaller transversedimension, as indicated by the arrow 11 in the branch '4. It andbranches may also be constituted by coaxial cable or some other suitabletype of transmission line. In the ring 10, the smaller transversedimension of the guide is parallel with the plane of the ring. Thebranches are connected to the ring 10 in the electric plane; that is,they branch from a wider side of the ring and the smaller transversedimension of each branch is parallel with the plane of the ring. Thiscorresponds to a series electrical connection. The ring 10 has a meancircumference equal to wavelengths A within the guide at a selecteddesign frequency f and, therefore, the branches 1 to 6 have a spacingaround the ring of A/ 4 between centers. Each of the branches has thesame characteristic impedance Z of another embodiment of The wave guideforming the ring 10 has a characteristicimpedance equal to Z /x/f. Thebranch 6 is terminated in an impedance Z which may, for example, beprovided by inserting a block 12 of dissipative material, preferablytapered at its inner end, as shown, to prevent reflection.

The hybrid ring just described may, for example, be used to obtain thesum of and ditference between two coherent voltages of frequency f. Ifthe voltages are applied to the arms 2 and 4, a voltage proportional totheir complex sum will appear at the arm 3, and a voltage proportional.to their complex difference will appear at the arm 1 and also at thearm 5. However, if the input voltages deviate from the frequency f, theoutput voltages at the arms 1 and 5 will be oppositely phased and mayv asort of. first-orderbe combined differentially to provide cancellationof frequency sensitivity, thus increasing the useful frequency band ofthe network. Even without the auxiliary path 7, if the arms 1 to 6 areall iteratively terminated there will be an impedance match with thering 10 at each of the branching points, but a considerable part of theinput power will be dissipated in the termination 12 of the arm 6.

This power loss is substantially eliminated by connecting the arms 3 and6 through an auxiliary path 7 extending across the ring 10. As shown,the path 7 is a series-connected, hollow-pipe wave guide having aneffective electrical length of )\/4. The required electrical length maybe obtained by placingwithin the guide 7 a properly dimensioned core 13of suitable dielectric material, if necessary. The characteristicimpedance of the path 7 is so chosen that the input voltage arrivingthereover at the arm 6 will be substantially equal to the voltagearriving at the arm 6 via the ring 10. Due to the half-wave differencebetween the length of the path 7 and the half-perimeter of the ring 10,these voltages will be 1r radians out of phase with each other and,since they are equal, will tend to cancel, leaving substantially no netvoltage on the arm 6. Therefore, only a negligible electric fieldparallel to the is to be understood that the ring iteratively terminatedin a dissipative block 16, corresponding to the termination 12 inFIG. 1. The auxiliary path connecting the arms 3 and 6 is provided bythe coupling apertures 19 and 20 which extend through the adjacent wallsof the portions 17 and 18. The apertures 19 and 20 are of equal area andare spaced apart a distance equal to 7\/4 at the frequency f toconstitute a directional coupler of the type disclosed in greaterdetail, for example, in United States Patent No. 2,562,281, to W. W.Mumford, issued July 31, 1951. The desired compensating voltage isobtained from the arm 3 by means of a directional coupler so that noimpedance irregularities will be introduced into the arm.

In order to prevent loss of input power by dissipation in thetermination 16, it is required that the voltage efiective thereonderived from the arm 3 shall be equal in magnitude to, but 1r radiansout of phase with, the voltage at that point derived from the ring 15 bythe arm 6, so that these two voltages will cancel each other. This issubstantially accomplished by so choosing the areas of the apertures 19*and 20 that these voltages are equal, andby making the length of the arm6 such that the voltages'will be 1r radians out of phase.

It is to' be understood that the above-described arrangements areillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention. Forexample, the transmission line may be of a different type than waveguide, the length of the ring can be other than 3M2, and some or all ofthe arms can be connected to the ring in shunt instead of in series.Explicit rules to be followed in making these latter modifications aregiven in the Tyrrell paper and in my copending application cited above.

What is claimed is:

1'. A network comprising a closed transmission loop having an effectivelength of wavelengths at a selected design frequency, six transmissionbranches connected in series with said loop at equally spaced pointsthereon, a matching termination for one of said branches, and means forsubstantially preventing the dissipation of power in said terminationcomprising an auxiliary transmission path connecting said one branch andthe branch opposite th re o.

2. A network in accordance with claim 1 in which said auxiliary pathextends across said loop.

3. A network in accordance with claim 2 in which said auxiliary path hasa length equal to a quarter wavelength at said frequency.

4. A network in accordance with claim 2 in which said auxiliary path isconstituted by a wave guide and said wave guide has a core of dielectricmaterial.

5. A network in accordance with claim 1 in which said auxiliary pathincludes a directional coupler.

6. A network in accordance with claim 1 in which said one branch has a"portion lying alongside a portion of said opposite branch, and saidauxiliary path includes a directional coupler coupling said portions.

7. A network in accordance with claim 6 in which said directionalcoupler includes two apertures of equal area extending through adjacentwalls of said portions.

8. A network in accordance with claim 7 in which said apertures arespaced apart a distance equal to a quarter wavelength at said frequency.

9. A network in accordance with claim 1 in which said loop isconstituted by a wave guide.

10. A network in accordance with claim 9 in which said wave guide isoblong in cross section and the smaller transverse dimension of saidguide is parallel with the plane of said loop.

11. A network in accordance with claim 1 in which each of said brancheshas a characteristic impedance Z and said loop has a characteristicimpedance equal to Z /2.

12. A network in accordance with claim 1 in which said termination isconstituted by a block of dissipative material.

13. A network in accordance with claim 12 in which said block is taperedat its inner end.

References Cited in the file of this patent UNITED STATES PATENTS RingMar. 31, 19 53

